Problem: Simplify the following expression: $k = \dfrac{1}{8a} - \dfrac{1}{3a}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $8a$ and $3a$ $\lcm(8a, 3a) = 24a$ $ k = \dfrac{3}{3} \cdot \dfrac{1}{8a} - \dfrac{8}{8} \cdot \dfrac{1}{3a} $ $k = \dfrac{3}{24a} - \dfrac{8}{24a}$ $k = \dfrac{3 -8}{24a}$ $k = \dfrac{-5}{24a}$